In heretofore known pressure responsive, pilot actuated, modulating valves as exemplified in the U.S. Pat. Nos. to Harris, 2,575,272; Olson 2,968,464 and Keller 3,405,906, wherein a movable main valve element of a main valve assembly is positioned by an actuating element, such as a piston, diaphragm or bellows, which responds to the positioning of a pilot valve assembly by utilizing the force of the pressure in the fluid, the flow of which is to be controlled, there exists the problem of stability of operation. In such valves, the lifting or unseating force must equal the opposing forces for modulation. This balance is upset by the flow forces of the fluid to be controlled, as for example, the flow of liquid, gas or steam, thus causing instability. This stability of valve operation can be achieved to a limited extent by sizing of orifices, pilot valve assembly configuration, increasing dampening and reduction or control chamber volume. Valve operational stability is particularly difficult to achieve where the fluid to be controlled is a gaseous fluid, as for example air or steam.
Accordingly, it is an object of this invention to provide a pressure responsive, pilot actuated, modulating valve which has a higher degree of stability of operation than heretofore known valves of this type.
Another object to the prsent invention is to provide a pressure responsive, pilot actuated, modulating valve in which chattering is minimized.
A still further object of this invention is to provide a pressure responsive, pilot actuated, modulating valve which is of relatively simple and compact construction.
For convenience, valve mechanisms or assemblies will sometimes be identified by reference only to their movable portions or members (e.g. the plug elements) as distinguished from the entire valve assembly consisting of the movable plug element, port and seat. Where reference is intended to encompass the entire assembly, the word "assembly" will be used.